1. Field of the Invention
The invention is directed to a hydrodynamic clutch device with a hydrodynamic circuit including a turbine wheel and an impeller wheel and a residual circuit including a lockup clutch for selectively fixing the turbine wheel relative to a drive.
2. Description of the Related Art
A hydrodynamic clutch device in the form of a torque converter, whose hydrodynamic circuit comprises an impeller, turbine and stator, is known from German reference DE 41 21 586 Al, particularly from FIG. 1 and the associated part of the specification. Apart from this hydrodynamic circuit, the clutch housing further comprises a lockup clutch which is provided for fixing the turbine wheel relative to a drive, e.g., the crankshaft of an internal combustion engine, and which is supplied via a hydraulic supply system with switchable pressure medium lines for controlling the lockup clutch. A torsional vibration damper acting between the lockup clutch and the turbine wheel is also provided.
In hydrodynamic clutch devices of this type, the hydrodynamic circuit is bridged increasingly earlier for reasons pertaining to wear and, as the case may be, is utilized purely as a starting element. Since many drives, particularly internal combustion engines, generate relatively large torsional vibrations at comparatively low speeds, the earlier bridging times require that these torsional vibrations at low speeds must be compensated in the torsional vibration damper, so that torsional vibration dampers of increasingly larger volume are used. In view of the fact that the lockup clutch offers only very little leeway in terms of design for gaining axial installation space, a large torsional vibration damper can be carried out only at the expense of the axial extension of the hydrodynamic circuit. This results in hydrodynamic circuits which are increasingly narrower in the axial direction which leads to a reduced through-flow cross section between the other and inner torus and to decreased throughput, thereby reducing the starting torque of the torque converter. One solution is to axially flatten the construction of the inner torus. However, in conjunction with the axially narrow construction of the outer torus, this would produce flow problems between the individual running wheels, such as partial reflux and dead zones for flow, reducing the efficiency of the hydrodynamic circuit. Therefore, this solution increases starting torque at the cost of reduced efficiency.
In torque converters, the starting torque may also be influenced by the blade angle of the running wheels. However, an adjustment of the blade angles also affects the starting transmission ratio, which can have negative consequences depending on the intended use of the torque converter.
A further solution for increasing the starting torque is to increase the diameter of the hydrodynamic circuit, so that, as a result of the dependence of the pump torque on the outer diameter of the hydrodynamic circuit as D.sup.5, the starting torque of the pump can be appreciably increased by only a slight increase in diameter. However, the increased inertia in the running wheels and the greater radial installation space requirement of even a slight increase in diameter are disadvantageously noticeable.
Hydraulic clutches which have narrower axial dimensions owing to the absence of the stator wheel and which also usually have a hydrodynamic circuit with a comparatively small cross section may be used as an alternative to torque converters. Compared with a torque converter, hydraulic clutches of this type have the disadvantage that there is no starting gear multiplication due to the absence of the stator. Further, the starting torque in hydraulic clutches of the type mentioned above is small, especially when the hydrodynamic circuit has a small cross section because of the small diameter ratio between the outer and inner diameter of the impeller and turbine.